1. Field of the Invention
The present invention relates to a method of manufacturing a glass preform added with an additive.
2. Description of the Related Art
Conventionally, glass preforms added with additives, which are used as optical fiber preforms and the like, are manufactured as follows. First, a porous glass preform is formed by a vapor-phase synthesis method such as vaporphase axial deposition (VAD) method or outside vapor deposition (OVD) method. The porous glass preform formed is immersed in an additive solution with an additive-containing compound dissolved in a predetermined solvent to impregnate the additive solution into fine pores in the porous glass preform. Next, the porous glass preform is dried to evaporate the solvent and to make the additive remain in the pores. Lastly, the porous glass preform is sintered to be transparently vitrified and formed into a glass preform (see Japanese Patent Publication No. 558-003980).
Further, a method of adding a rare earth element in high Concentration in a center portion of a glass preform in manufacturing an optical fiber preform doped with the rare earth element to manufacture, for example, an optical-amplification optical fiber has been disclosed (see Japanese Patent Application Laid-open No. H7-109144).
In recent years, along with an increasing demand for high-performance like suppression of nonlinear phenomena in optical fibers and for reduction in cost, a demand for addition of a larger quantity of an additive in the optical fibers is increasing. However, conventionally, increasing the additive concentration in the additive solution has been the only way to increase the quantity of addition, and it has been difficult to efficiently add the additive.